# Nimbo City audio credits

Source licenses are listed per asset: CC0-1.0 for the motors and police recording,
CC BY 4.0 for the ambulance and fire-truck recordings. Local copies are edited from
the public high-quality previews, not claimed to be the original lossless files.
There are no remote sound requests while playing. Attribution is also accessible
in the profile under “Geluid en makers”.

CC0: https://creativecommons.org/publicdomain/zero/1.0/
CC BY 4.0: https://creativecommons.org/licenses/by/4.0/

## car-engine.wav

**engine_idle.wav** — mhad
https://freesound.org/people/mhad/sounds/390788/

Recorded vehicle engine idle.
Trimmed, DC removed, wrap seam smoothed, soft-limited and normalized to 0.78 peak.

## diesel-engine.wav

**Truck Engine Idle Loops.flac** — qubodup
https://freesound.org/people/qubodup/sounds/187564/

Construction vehicle engine recording extracted from a US government video.
Trimmed, DC removed, wrap seam smoothed, soft-limited and normalized to 0.78 peak.

## nl-police-siren.wav — CC0-1.0

**Dutch night ambience with scooter passing, train and police siren** —
hz37 (Hens Zimmerman Audio), Bilthoven, Netherlands. Published 14 March 2025.
https://freesound.org/people/hz37/sounds/792488/

Actual police siren recorded with a Zoom h4n in X/Y stereo. The siren section
at 108.2–113.4 seconds is extracted; the opening scooter pass is excluded.
Used for police, police van and coastguard boat.

## nl-ambulance-siren.wav — CC BY 4.0

**Ambulance.wav** — LG, Rotterdam, Netherlands. Published 4 February 2006.
https://freesound.org/people/LG/sounds/15430/
License: https://creativecommons.org/licenses/by/4.0/

Actual ambulance passing at speed, recorded with an Olympus VN 480.
The section at 2.3–7.1 seconds is extracted. This historical field recording
already contains traffic, distortion and natural Doppler; it is not a studio
recording or a claim about every ambulance's current siren.
Used for ambulance and rapid responder.

## nl-fire-siren.wav — CC BY 4.0

**Fire-truck large.WAV** — Sandermotions. Published 19 January 2017.
https://freesound.org/people/Sandermotions/sounds/377125/
License: https://creativecommons.org/licenses/by/4.0/

Actual large Dutch fire-truck siren recorded with a Zoom H1.
The section at 7.8–12.62 seconds is extracted; opening handling noise is excluded.
Used for fire engine and ladder truck.

All three siren recordings are mixed to mono at 48 kHz, trimmed, filtered,
DC removed, gently soft-limited, peak-normalized and crossfaded for looping.
Their pitches and natural rhythms are retained. Passing vehicles add spatial
attenuation, stereo placement and simulated Doppler; the player's siren has no
artificial vehicle-specific pitch adjustment. Natural Doppler in the source
recordings remains. Exact source URLs, hashes, trim times and processing details
are recorded in `audio.json`; `scripts/prepare-siren-audio.py` rebuilds the loops.

These recordings replace the former synthesizer-generated siren by QuickSilver99;
that file is no longer distributed. If a sample temporarily fails to load, an
available actual siren recording is used until retry succeeds. Procedural audio
is retained only as a last fallback when no recording is available.